Electric arc welder system with waveform profile control for cored electrodes

ABSTRACT

An electric arc welder for creating a welding process in the form of a succession of AC waveforms between a particular type of cored electrode, with a sheath and core, and a workpiece by a power source comprising a high frequency switching device for creating the individual waveforms in the succession of waveforms, each waveform having a profile is formed by the magnitude of each of a large number of short current pulses generated at a frequency of at least 18 kHz where the profile is determined by the input signal to a wave shaper controlling the short current pulses; a circuit to create a profile signal indicative of the particular type of electrode; and a select circuit to select the input signal based upon the profile signal whereby the wave shaper causes the power source to create a specific waveform profile for the particular type of cored electrode.

REFERENCE TO RELATED APPLICATION

This application is a continuation of, and claims priority to and thebenefit of, co-pending U.S. patent application Ser. No. 11/615,559,filed Dec. 22, 2006, which is a continuation of, and claims priority toand the benefit of, U.S. patent application Ser. No. 10/834,141, filedApr. 29, 2004, now U.S. Pat. No. 7,166,817, both entitled ELECTRIC ARCWELDER SYSTEM WITH WAVEFORM PROFILE CONTROL FOR CORED ELECTRODES, theentirety of which are hereby incorporated by reference.

The present invention relates to the art of electric arc welding andmore particularly to an electric arc welder with waveform profilecontrol for cored electrodes used in pipeline welding, primarilyoff-shore pipeline welding.

INCORPORATION BY REFERENCE

The present invention is directed to an electric arc welder systemutilizing high capacity alternating circuit power sources for drivingtwo or more tandem electrodes of the type used in seam welding of largemetal blanks, such as pipelines. It is preferred that the power sourcesuse the switching concept disclosed in Stava U.S. Pat. No. 6,111,216wherein the power supply is an inverter having two large output polarityswitches with the arc current being reduced before the switches reversethe polarity. Consequently, the term “switching point” is a complexprocedure whereby the power source is first turned off awaiting acurrent less than a preselected value, such as 100 amperes. Uponreaching the 100 ampere threshold, the output switches of the powersupply are reversed to reverse the polarity from the D.C. output link ofthe inverter. Thus, the “switching point” is an off output command,known as a “kill” command, to the power supply inverter followed by aswitching command to reverse the output polarity. The kill output can bea drop to a decreased current level. This procedure is duplicated ateach successive polarity reversal so the AC power source reversespolarity only at a low current. In this manner, snubbing circuits forthe output polarity controlling switches are reduced in size oreliminated. Since this switching concept is preferred to define theswitching points as used in the present invention, Stava U.S. Pat. No.6,111,216 is incorporated by reference. The concept of an AC current fortandem electrodes is well known in the art. U.S. Pat. No. 6,207,929discloses a system whereby tandem electrodes are each powered by aseparate inverter type power supply. The frequency is varied to reducethe interference between alternating current in the adjacent tandemelectrodes. Indeed, this prior patent of assignee relates to singlepower sources for driving either a DC powered electrode followed by anAC electrode or two or more AC driven electrodes. In each instance, aseparate inverter type power supply is used for each electrode and, inthe alternating current high capacity power supplies, the switchingpoint concept of Stava U.S. Pat. No. 6,111,216 is employed. This systemfor separately driving each of the tandem electrodes by a separate highcapacity power supply is background information to the present inventionand is incorporated herein as such background. In a like manner, U.S.Pat. Nos. 6,291,798 and 6,207,929 disclose further arc welding systemswherein each electrode in a tandem welding operation is driven by two ormore independent power supplies connected in parallel with a singleelectrode arc. The system involves a single set of switches having twoor more accurately balanced power supplies forming the input to thepolarity reversing switch network operated in accordance with Stava U.S.Pat. No. 6,111,216. Each of the power supplies is driven by a singlecommand signal and, therefore, shares the identical current valuecombined and directed through the polarity reversing switches. This typesystem requires large polarity reversing switches since all of thecurrent to the electrode is passed through a single set of switches.U.S. Pat. No. 6,291,798 does show a master and slave combination ofpower supplies for a single electrode and discloses general backgroundinformation to which the invention is directed. For that reason, thispatent is also incorporated by reference. An improvement for operatingtandem electrodes with controlled switching points is disclosed inHouston U.S. Pat. No. 6,472,634. This patent is incorporated byreference.

The present invention relates to coordination of a specific waveformprofile for an AC waveform, which profile is coordinated with aparticular cored electrode used in welding, such as pipeline welding.Such welding normally uses DC positive or DC negative, especially whenusing a cored electrode. There is one exception where a cored electrodehas been tried. In the prior art, a cored electrode has been suggestedfor use in conjunction with a STT waveform which waveform can bepositive or negative. In an illustration the process alternates betweenSTT positive and a STT negative. This concept is not AC, but is shown inStava U.S. Pat. No. 6,051,810, which is incorporated by reference hereinas background information.

BACKGROUND OF INVENTION

Welding applications, such as pipe welding, often require high currentsand use several arcs created by tandem electrodes. Such welding systemsare quite prone to certain inconsistencies caused by arc disturbancesdue to magnetic interaction between two adjacent tandem electrodes. Asystem for correcting the disadvantages caused by adjacent AC driventandem electrodes is disclosed in Stava U.S. Pat. No. 6,207,929. In thatprior patent, each of the AC driven electrodes has its own inverterbased power supply. The output frequency of each power supply is variedso as to prevent interference between adjacent electrodes. This systemrequires a separate power supply for each electrode. As the currentdemand for a given electrode exceeds the current rating of the inverterbased power supply, a new power supply must be designed, engineered andmanufactured. Thus, such system for operating tandem welding electrodesrequire high capacity or high rated power supplies to obtain highcurrent as required for pipe welding. To decrease the need for specialhigh current rated power supplies for tandem operated electrodes,assignee developed the system disclosed in Stava U.S. Pat. No. 6,291,798wherein each AC electrode is driven by two or more inverter powersupplies connected in parallel. These parallel power supplies have theiroutput current combined at the input side of a polarity switchingnetwork. Thus, as higher currents are required for a given electrode,two or more parallel power supplies are used. In this system, each ofthe power supplies are operated in unison and share equally the outputcurrent. Thus, the current required by changes in the welding conditionscan be provided only by the over current rating of a single unit. Acurrent balanced system did allow for the combination of several smallerpower supplies; however, the power supplies had to be connected inparallel on the input side of the polarity reversing switching network.As such, large switches were required for each electrode. Consequently,such system overcame the disadvantage of requiring special powersupplies for each electrode in a tandem welding operation of the typeused in pipe welding; but, there is still the disadvantage that theswitches must be quite large and the input, paralleled power suppliesmust be accurately matched by being driven from a single current commandsignal. Stava U.S. Pat. No. 6,291,798 does utilize the concept of asynchronizing signal for each welding cell directing current to eachtandem electrode. However, the system still required large switches.This type of system was available for operation in an Ethernet networkinterconnecting the welding cells. In Ethernet interconnections, thetiming cannot be accurately controlled. In the system described, theswitch timing for a given electrode need only be shifted on a timebasis, but need not be accurately identified for a specific time. Thus,the described system requiring balancing the current and a single switchnetwork has been the manner of obtaining high capacity current for usein tandem arc welding operations when using an Ethernet network or aninternet and Ethernet control system. There is a desire to controlwelders by an Ethernet network, with or without an internet link. Due totiming limitation, these networks dictated use of tandem electrodesystems of the type using only general synchronizing techniques.

Such systems could be controlled by a network; however, the parameter toeach paralleled power supply could not be varied. Each of the cellscould only be offset from each other by a synchronizing signal. Suchsystems were not suitable for central control by the internet and/orlocal area network control because an elaborate network to merelyprovide offset between cells was not advantageous. Houston U.S. Pat. No.6,472,634 discloses the concept of a single AC arc welding cell for eachelectrode wherein the cell itself includes one or more paralleled powersupplies each of which has its own switching network. The output of theswitching network is then combined to drive the electrode. This allowsthe use of relatively small switches for polarity reversing of theindividual power supplies paralleled in the system. In addition,relatively small power supplies can be paralleled to build a highcurrent input to each of several electrodes used in a tandem weldingoperation. The use of several independently controlled power suppliesparalleled after the polarity switch network for driving a singleelectrode allows advantageous use of a network, such as the internet orEthernet.

In Houston U.S. Pat. No. 6,472,634, smaller power supplies in eachsystem are connected in parallel to power a single electrode. Bycoordinating switching points of each paralleled power supply with ahigh accuracy interface, the AC output current is the sum of currentsfrom the paralleled power supplies without combination before thepolarity switches. By using this concept, the Ethernet network, with orwithout an internet link, can control the weld parameters of eachparalleled power supply of the welding system. The timing of the switchpoints is accurately controlled by the novel interface, whereas the weldparameters directed to the controller for each power supply can beprovided by an Ethernet network which has no accurate time basis. Thus,an internet link can be used to direct parameters to the individualpower supply controllers of the welding system for driving a singleelectrode. There is no need for a time based accuracy of these weldparameters coded for each power supply. In the preferred implementation,the switch point is a “kill” command awaiting detection of a currentdrop below a minimum threshold, such as 100 amperes. When each powersupply has a switch command, then they switch. The switch points betweenparallel power supplies, whether instantaneous or a sequence involving a“kill” command with a wait delay, are coordinated accurately by aninterface card having an accuracy of less than 10 μs and preferably inthe range of 1-5 μs. This timing accuracy coordinates and matches theswitching operation in the paralleled power supplies to coordinate theAC output current.

By using the internet or Ethernet local area network, the set of weldparameters for each power supply is available on a less accurateinformation network, to which the controllers for the paralleled powersupplies are interconnected with a high accuracy digital interface card.Thus, the switching of the individual, paralleled power supplies of thesystem is coordinated. This is an advantage allowing use of the internetand local area network control of a welding system. The informationnetwork includes synchronizing signals for initiating several arcwelding systems connected to several electrodes in a tandem weldingoperation in a selected phase relationship. Each of the welding systemsof an electrode has individual switch points accurately controlled whilethe systems are shifted or delayed to prevent magnetic interferencebetween different electrodes. This allows driving of several ACelectrodes using a common information network. The Houston U.S. Pat. No.6,472,634 system is especially useful for paralleled power supplies topower a given electrode with AC current. The switch points arecoordinated by an accurate interface and the weld parameter for eachparalleled power supply is provided by the general information network.This background is technology developed and patented by assignee anddoes not necessarily constitute prior art just because it is herein usedas “background.”

As a feature of the system in Stava U.S. Pat. No. 6,207,929, two or morepower supplies can drive a single electrode. Thus, the system comprisesa first controller for a first power supply to cause the first powersupply to create an AC current between the electrode and workpiece bygenerating a switch signal with polarity reversing switching points ingeneral timed relationship with respect to a given system synchronizingsignal received by the first controller. This first controller isoperated at first welding parameters in response to a set of first powersupply specific parameter signals directed to the first controller.There is provided at least one slave controller for operating the slavepower supply to create an AC current between the same electrode andworkpiece by reversing polarity of the AC current at switching points.The slave controller operates at second weld parameters in response tothe second set of power supply specific parameter signals to the slavecontroller. An information network connected to the first controller andthe second or slave controller contains digital first and second powersupply specific parameter signals for the two controllers and the systemspecific synchronizing signal. Thus, the controllers receive theparameter signals and the synchronizing signal from the informationnetwork, which may be an Ethernet network with or without an internetlink, or merely a local area network. The invention involves a digitalinterface connecting the first controller and the slave controller tocontrol the switching points of the second or slave power supply by theswitch signal from the first or master controller. In practice, thefirst controller starts a current reversal at a switch point. This eventis transmitted at high accuracy to the slave controller to start itscurrent reversal process. When each controller senses an arc currentless than a given number, a “ready signal” is created. After a “ready”signal from all paralleled power supplies, all power supplies reversepolarity. This occurs upon receipt of a strobe or look command each 25μs. Thus, the switching is in unison and has a delay of less than 25 μs.Consequently, both of the controllers have interconnected datacontrolling the switching points of the AC current to the singleelectrode. The same controllers receive parameter information and asynchronizing signal from an information network which in practicecomprises a combination of internet and Ethernet or a local areaEthernet network. The timing accuracy of the digital interface is lessthan about 10 μs and, preferably, in the general range of 1-5 μs. Thus,the switching points for the two controllers driving a single electrodeare commanded within less than 5 μs. Then, switching actually occurswithin 25 μs. At the same time, relatively less time sensitiveinformation is received from the information network also connected tothe two controllers driving the AC current to a single electrode in atandem welding operation. The 25 μs maximum delay can be changed, but isless than the switch command accuracy.

The unique control system disclosed in Houston U.S. Pat. No. 6,472,634is used to control the power supply for tandem electrodes used primarilyin pipe seam welding and disclosed in Stava U.S. Pat. No. 6,291,798.This Stava patent relates to a series of tandem electrodes movable alonga welding path to lay successive welding beads in the space between theedges of a rolled pipe or the ends of two adjacent pipe sections. Theindividual AC waveforms used in this unique technology are created by anumber of current pulses occurring at a frequency of at least 18 kHzwith a magnitude of each current pulse controlled by a wave shaper. Thistechnology dates back to Blankenship U.S. Pat. No. 5,278,390. Shaping ofthe waveforms in the AC currents of two adjacent tandem electrodes isknown and is shown in not only the patents mentioned above, but in StavaU.S. Pat. No. 6,207,929. In this latter Stava patent, the frequency ofthe AC current at adjacent tandem electrodes is adjusted to preventmagnetic interference. All of these patented technologies by The LincolnElectric Company of Cleveland, Ohio have been advances in the operationof tandem electrodes each of which is operated by a separate AC waveformcreated by the waveform technology set forth in these patents. Thesepatents are incorporated by reference herein. However, these patents donot disclose the present invention which is directed to the use of aunique implementation of waveform technology to create a specificwaveform for use in welding using an AC current and a cored electrode.

When using the waveform technology as so far described for off-shorewelding or welding on pipelines, the welding process generally usedsolid welding wires with a shielding gas. In this type of process, DCwelding as described, together with STT welding has been the normalpractice. When cored electrodes are used, the core can be formed ofalloy material to make the weld metal. Such processes generally requiredDC welding using cored electrodes. Consequently, in the past cored orsolid wire using a DC process with external shielding gas has been thenormal practice, especially for off-shore welding and pipeline welding.The DC welding presented little problems of uneven burn back of thesheath and core. The electrodes were cored for alloying. The need forcontrolled strength and hardness combined with low diffusible hydrogenlimits made it difficult to use AC welding. These DC welding processeshave been used in the field and are the background to which the presentinvention is directed. There has been no use of cored electrodes and ACwelding because the AC waveforms were not tailored to any particularcored electrode. The burn rate for the sheath and core could not becontrolled.

THE INVENTION

The present invention is used with a cored electrode having a specialconstructed AC waveform generated between the cored electrode andworkpiece, which special AC waveform is outputted in succession toconstitute the welding process. By using the present invention thewaveform in the AC welding process is controlled in a unique manner thatadjusts several profile parameters and also the energy profile of theindividual sections of the waveform. The waveform is coordinated with aspecific cored electrode so the sheath and core burn back at the provenrate. AC welding could not be used successfully for a cored electrode.The creation of a special profile for the waveform affects the overallwelding process in a unique manner that accurately controls the processusing waveform technology of the type pioneered by The Lincoln ElectricCompany of Cleveland, Ohio. By using the present invention, the weldingprocess is controlled to affect several characteristics, such aspenetration into the base metal, the melt off rate of the electrode, theheat input into the base metal, and the welding travel speed as well asthe wire feed speed while using AC welding with a cored electrode. Inaddition, the arc welding current and/or arc welding voltage waveform isgenerated to essentially “paint” a desired waveform for coordinationwith a given cored electrode to affect the mechanical and metallurgicalproperties of the “as welded” weld metal resulting from the weldingprocess. The invention selects the profile of an AC waveform for a givenelectrode. By having the ability to accurately control the exact profileof the AC waveform, this invention is made possible.

In the past DC welding was the norm. In the past DC welding of pipelinewas normal. To use AC welding so the heat would be controlled oradjusted there was still a need for shielding gas which could blow awayin high winds. To reduce heat the wire feed speed had to be reduced. ACwelding could control heat, but could not be used with cored electrodes.The invention allows use of cored electrodes with AC welding and whenusing a cored electrode, reducing the problems of high winds.

When coordinating various welding waveforms, sometimes called waveshapes, with specific cored electrodes, an improvement in the weldingprocess both in welding speed and improved mechanical and metallurgicalproperties is obtained. The actual electrode is combined with the uniqueprofile controlled AC waveforms to produce the required welding resultsheretofore obtainable by only DC welding. By coordinating the desiredwelding wire and a specific exactly controlled general AC profile of anindividual waveform in a succession of waveforms constituting thewelding process, the welder using the present invention can produceheretofore unobtainable weld results. This provides a unique AC weldingprocess usable in off-shore welding and pipeline welding.

In accordance with the present invention there is provided an electricarc welder for creating a succession of AC waveforms between a coredelectrode and a workpiece by a power source comprising a high frequencyswitching device such as an inverter or its equivalent chopper forcreating individual waveforms in the succession of waveformsconstituting the welding process. Each of the individual waveforms has aprecise general profile determined by the magnitude of each of a largenumber of short current pulses generated at a frequency of at least 18kHz by a pulse width modulator with the magnitude of the current pulsescontrolled by a wave shaper. The polarity of any portion of theindividual AC waveform is determined by the data of a polarity signal. Aprofile control network is used for establishing the general profile ofan individual waveform by setting more than one profile parameter of theindividual waveform. The parameters are selected from the classconsisting of frequency, duty cycle, up ramp rate and down ramp rate.Also included in the welder control is a magnitude circuit for adjustingthe individual waveform profile to set total current, voltage and/orpower for the waveform without substantially changing the set generalprofile. This concept of the invention is normally accomplished in twosections where the energy is controlled in the positive polarity and inthe negative polarity of the generated waveform profile.

In accordance with another aspect of the present invention there isprovided a method of electric arc welding by creating a succession of ACwaveforms between a cored electrode and a workpiece by a power sourcecomprising a high frequency switching device for creating individualwaveforms in the succession of waveforms constituting the weld process.Each of the individual waveforms has profile determined by the magnitudeof each of a large number of short current pulses generated at afrequency of at least 18 kHz by a pulse width modulator with themagnitude of the current pulses controlled by a wave shaper. The methodcomprises determining the plurality of any portion of the individualwaveform by the data of a plurality signal, establishing the generalprofile of an individual waveform by setting more than one profileparameter of an individual waveform, the parameters selected from theclass consisting of frequency, duty cycle, up ramp rate and down ramprate and adjusting the waveform to set the total magnitude of current,voltage and/or power without substantially changing the set profile.

In the past, the off-shore and pipe welding was normally limited to asingle polarity using a gas shielded metal wire. Such shielding isdifficult to control in windy conditions often experienced in off-shoreand pipeline welding. Consequently, there is a substantial need for awelding process using self shielding electrodes such as FCAW-SS wiretechnology. The sheath on the electrode and the inner flux core must bemelted at the same rate while maintaining the same wire feed speedwithout introducing undesirable arc instability. Furthermore heat cannotbe adjusted. Consequently, there is a desire for an AC waveform so theduty cycle of either the negative or positive portion of the waveform iscontrolled to adjust the melting rate and heat to the weld pool duringthe welding operation. All of these difficulties have generally limitedthe use of AC welding with a cored, self shielded electrode. Theadvantage of AC welding with the advantage of cored self shielding wasnot obtainable on a consistent basis. The waveforms, especially whendeveloped by waveform technology, have to be different for eachdifferent cored electrode. Thus, the use of a standard AC arc welderwith cored electrode having self shielding capabilities has not beenavailable in the past. The present invention allows the use of coredself shielding electrodes with AC welding, which combination is noveland is accomplished to optimize the actual welding result by correlatingthe waveform and a specific electrode.

The invention accomplishes AC welding with cored self shieldingelectrodes to achieve superior productivity and mechanical properties bylowering the heat input per unit of deposition and by shortening the arclength to reduce atmospheric contamination. This has not beenaccomplished before in pipeline welding. The invention allows the use ofa welding operation involving AC waveforms in a manner that canaccomplish a short arc length to prevent atmospheric contamination.Furthermore, by using a self shielding electrode, the atmospheric windcannot blow away the shielding gas as is experienced in FCAW-G welding.The invention is the development of a new welding system making possiblethe use of cored electrodes. This is accomplished with an AC arc weldingpower source. The benefits of both a cored electrode and AC welding areobtained. The AC power source, in accordance with the invention, iscapable of generating a wave shape of virtually any form and is notlimited to simply an AC sine wave or square wave. The AC waveform has aspecific profile that is coordinated with an exact cored electrode tooptimize the waveform profile for the electrode being used in thewelding process. In accordance with an aspect of the invention, thewaveform has an unbalanced relationship so that the positive andnegative polarity portions of the welding process heat and depositmolten metal in a different manner to optimize the AC welding process.By using the present invention, the constituents of the core material ofthe electrode is selected to achieve optimum results for the weld metal,in terms of metallurgical and mechanical properties of the “as welded”material. In other words, the electrode core chemistry is modified totake advantage of the various AC waveforms produced by the AC arcwelding power source by coordinating the waveforms with the chemistry ofthe core. This has never been accomplished before and allows the use ofcored electrodes with self shielding capability in off-shore pipelinewelding. Different polarity portions of the waveform produce differentwelding results for a given electrode in terms of heat input to thework, melt off rate of the electrode and the metallurgical andmechanical properties of the weld deposit. By using an AC welding powersource as described, in conjunction with a tubular electrode of the selfshielding type, superior welding results are achieved. The self shieldedelectrode does not require additional shielding gas and thereforeresults in additional savings in the welding process. Furthermore, thepower source uses waveform technology where the profile of the waveformcan be created. The profile can be selected based upon both the specificconstruction of the cored electrode and the wire feed speed of thewelding process. Consequently, a distinct advantage of the invention isthe ability to control the actual waveform of the AC welding process bythe specific cored electrode used and the set point of the welder. Thus,the invention provides significant benefits in the quality of the weldand also increases welding speed. Consequently, the production rateusing the present invention is increased.

The invention furthermore benefits application in the field of crosscountry pipeline welding, as well as off-shore welding of pipelines orother structures. In the pipe welding industry, it is well known thatthe weld quality and welding speed or production is of essence. In crosscountry and off-shore pipeline construction projects, it is well knownthat such projects normally include high hourly costs for theconstruction equipment. This is especially the case on off-shorepipeline projects, where the ships used for constructing the pipelinenormally lease at a cost of millions of dollars per day. Consequently,the welding of the pipeline must be done as quickly as possible with aminimum of repairs to minimize the cost factor in the process.Consequently, the AC welding process and the tubular cored electrodesignificantly benefit the industry in terms of producing high qualitywelds at a faster speed.

A broad aspect of the present invention is the tailoring or coordinatingof accurately profiled waveforms of an AC welding process with the exactchemistry and composition of the electrode. Thus, a given electrode isidentified to provide an identification signal. This signal is used toselect the exact coordinated AC waveform from many waveforms stored inthe power source. This concept of selecting the profile of the ACwaveform to match a specific cored electrode has not been heretoforeused. This process allows AC welding of a pipeline with a cored, selfshielded electrode.

In accordance with the present invention there is provided an electricarc welder for creating a welding process in the form of a succession ofAC waveforms between a particular type of cored electrode with a sheathand core and a workpiece by a power source. The power source comprises ahigh frequency switching device for creating the individual waveforms inthe succession of waveforms constituting the welding process. Eachwaveform has a profile that is formed by the magnitude of the largenumber of short current pulses generated at a frequency of at least 18kHz, where the profile is determined by the input signal to a waveshaper controlling the short current pulses. The invention involves acircuit to create a profile signal indicative of a particular typeelectrode and a select circuit to select the input signal based upon theprofile signal indicative of a specific electrode. In this manner, thewave shaper causes the power source to create a specific waveformprofile for a particular type of cored electrode. By coordinating theexact waveform with a particular cored electrode, a cored electrode isusable in an AC waveform welding process. This process was not generallyobtainable in the past.

In accordance with another aspect of the present invention there isprovided a method of welding with a specific cored electrode having asheath and core. The method comprises using a waveform with a specificprofile tailored for welding with a specific cored electrode, creating aseries of these selected waveforms to provide a welding process andwelding with the electrode using this selected welding process. Inaccordance with a limited aspect of the invention the created waveformis an AC waveform. Furthermore, the waveform can have a different shapefor the positive polarity and the negative polarity. In this manner, theone polarity involves a relatively low current for a longer period oftime. This maintains the arc length relatively short to reduce theamount of exposure to the atmosphere during the welding process. In thismodification of the invention, the waveform is an AC waveform so thatthe profile of the selected waveform of the method is accuratelycontrolled.

The primary object of the present invention is the provision of anelectric arc welder, wherein the waveform is created by waveformtechnology and is developed for a particular cored electrode so that anoff-shore pipeline welding process can be accomplished using FCAW-SSprocess.

Another object of the present invention is the provision of a method,wherein waveform technology is used to generate waveforms coordinatedwith a particular cored electrode.

Yet another object of the present invention is the provision of a welderand method, as defined above, which welder and method results in arelatively short arc length and is used in high wind conditions foroff-shore pipeline welding and pipeline welding in general.

Still a further object of the present invention is the provision of anelectric arc welder and method, as defined above, wherein the ACwaveform has a low heat polarity portion to obtain a short arc length.

Still another object of the present invention is the provision of awelder and method, as defined above, which welder and method utilizes acored electrode that can be operated DC positive, DC negative, butpreferably AC.

Another object of the present invention is the provision of an electricarc welder and method, as defined above, which welder and method can beused for AC open root welding and combines self shielding electrodeswith an AC waveform that is tailored to the particular electrode.

Still a further object of the present invention is the provision of anelectric arc welder and method, as defined above, which welder andmethod utilizes both the identification of a particular electrode andthe wire feed speed to select the desired tailored waveform.

Another object of the present invention is the provision of an electricarc welder that has the capabilities of accurately controlling theprofile of the waveform so the profile of the waveform can becoordinated with a given electrode, especially a cored electrode.

Yet another object of the present invention is the provision of anelectric arc welder and method, as defined above, which welder andmethod allow coordination between a self shielded electrode and awaveform of the programmable power source, either DC or AC. In thismanner, a waveform is programmed into the power source so superiorresults are accomplished when using the corresponding, matched coredelectrode.

Still a further object of the present invention is the provision of anelectric arc welder utilizing waveform technology, which welder iscapable of having a waveform that is tailored made for a specific coredelectrode. This is especially advantageous for a self shielded electrodewhen used in an AC welding process.

Yet another object of the present invention is the provision of anelectric arc welder and method, as defined above, which welder andmethod has a waveform coordinated with a self shielded electrode so thatthe sheath and core melts at substantially the same rate.

Yet a further object of the present invention is the provision of anelectric arc welder using waveform technology wherein the generalprofile of the individual waveforms constituting the AC welding processis accurately controlled to a given profile that will produce a weldwith desired mechanical and metallurgical properties with a specificcored electrode.

Another object of the present invention is the provision of an electricarc welder, as defined above, which electric arc welder generates aprecise controllable and changeable general profile for the waveform ofan AC welding process to thereby adjust the weld speed, deposition rate,heat input, mechanical and metallurgical properties and relatedcharacteristics to improve the quality and performance of the weldingprocess.

These and other objects and advantages will become apparent from thefollowing description taken together with the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram of a welding system that can be used toperform the present invention;

FIG. 2 is a wiring diagram of two paralleled power sources, each ofwhich include a switching output and can be used in practicing theinvention;

FIG. 3 is a cross sectional side view of three tandem electrodes of thetype controllable by the power source disclosed in FIGS. 1 and 2;

FIG. 4 is a schematic layout in block form of a welding system for threeelectrodes using the disclosure in Houston U.S. Pat. No. 6,472,634 andStava U.S. Pat. No. 6,291,798 and where one of the three power sourcesis used in forming a precise tailored waveform by the program as shownin FIG. 17;

FIG. 5 is a block diagram showing a single electrode driven by thesystem as shown in FIG. 4 with a variable pulse generator disclosed inHouston U.S. Pat. No. 6,472,634 and used for practicing the presentinvention;

FIG. 6 is a current graph for one of two illustrated synchronizingpulses and showing a balanced AC waveform for one tandem electrode;

FIG. 7 is a current graph superimposed upon a polarity signal havinglogic to determine the polarity of the waveform as used in a welder thatcan practice the present invention as shown in FIGS. 17, 21, AND 27;

FIG. 8 is a current graph showing a broad aspect of a waveform with aprofile controllable by the present invention to be optimum for a givencored electrode and outputted by the welder shown in FIGS. 21 and 27;

FIGS. 9 and 10 are schematic drawings illustrating the dynamics of theweld puddle during concurrent polarity relationships of tandemelectrodes;

FIG. 11 is a pair of current graphs showing the waveforms on twoadjacent tandem electrodes that can be generated by a background system;

FIG. 12 is a pair of current graphs of the AC waveforms on adjacenttandem electrodes with areas of concurring polarity relationships, whereeach waveform can be coordinated with a given electrode;

FIG. 13 are current graphs of the waveforms on adjacent tandemelectrodes wherein the AC waveform of one electrode is substantiallydifferent waveform of the other electrode to limit the time ofconcurrent polarity relationships;

FIG. 14 are current graphs of two sinusoidal waveforms for adjacentelectrodes operated by a background system to use different shapedwaveforms for the adjacent electrodes;

FIG. 15 are current graphs showing waveforms at four adjacent AC arcs oftandem electrodes shaped and synchronized in accordance with abackground aspect of the invention;

FIG. 16 is a schematic layout of a known software program to causeswitching of the paralleled power supplies as soon as the coordinatedswitch commands have been processed and the next coincident signal hasbeen created;

FIG. 17 is a block diagram of the program used in the computercontroller of the welder to control the actual profile of the waveformusing the disclosure and concepts shown in FIGS. 1-16, so a welderperforms in accordance with the preferred embodiment of the presentinvention, as shown in FIGS. 21 AND 27;

FIG. 18 is a schematically illustrated waveform used in explaining theimplementation of the present program shown in FIG. 17;

FIG. 19 is a side elevational view with a block diagram illustrating theuse of the preferred embodiment of the present invention;

FIG. 20 is an enlarged cross-sectioned pictorial view taken generallyalong line 20-20 of FIG. 19;

FIG. 21 is a block diagram disclosing the preferred embodiment of thepresent invention;

FIG. 22 is a graph of the current, voltage or power curve showing thewaveform used in the welding process when implementing the invention asshown in FIG. 21;

FIG. 23 is a graph similar to the graph of FIG. 22 illustrating certainmodifications in the created waveform capable of being obtained whenusing the preferred embodiment of the present invention;

FIG. 24 is an enlarged, schematic view representing a cored electrodewhere the sheath and core are melted at a different rate;

FIG. 25 is a view similar to FIG. 24 illustrating the disadvantage of afailure to employ the present invention for welding with coredelectrodes;

FIG. 26 is a view similar to FIGS. 24 and 25 showing the operation of awelding process using the present invention as illustrated in FIG. 21;and,

FIG. 27 is a block diagram showing a welder similar to the welder shownin FIG. 21 using a modification of the preferred embodiment of theinvention where a fixed cored electrode activates a given waveform to beoutputted from the waveform generator.

PREFERRED EMBODIMENT

Referring now to the drawings wherein the showings are for the purposeof illustrating a preferred embodiment of the invention only and not forthe purpose of limiting same, a background system for implementing theinvention is shown in detail in FIGS. 1, 2, 4, 5, and 16. FIGS. 2 and6-15 describe prior attributes of the disclosed background weldingsystems. The welder described in FIGS. 17 and 18 is used to constructthe precise profile of the waveforms used in the wave shaper or waveformgenerator as a profile tailored for a specific electrode shown in FIG.20. These electrode-determined profiles are used in practicing theinvention described by use of FIGS. 19-27.

Turning now to the background system to which the present invention isan improvement and/or an enhancement, FIG. 1 discloses a single electricarc welding system S in the form of a single cell to create analternating current as an arc at weld station WS. This system or cellincludes a first master welder A with output leads 10, 12 in series withelectrode E and workpiece W in the form of a pipe seam joint or otherwelding operation. Hall effect current transducer 14 provides a voltagein line 16 proportional to the current of welder A. Less time criticaldata, such as welding parameters, are generated at a remote centralcontrol 18. In a like manner, a slave following welder B includes leads20, 22 connected in parallel with leads 10, 12 to direct an additionalAC current to the weld station WS. Hall effect current transducer 24creates a voltage in line 26 representing current levels in welder Bduring the welding operation. Even though a single slave or followerwelder B is shown, any number of additional welders can be connected inparallel with master welder A to produce an alternating current acrosselectrode E and workpiece W. The AC current is combined at the weldstation instead of prior to a polarity switching network. Each welderincludes a controller and inverter based power supply illustrated as acombined master controller and power supply 30 and a slave controllerand power supply 32. Controllers 30,32 receive parameter data andsynchronization data from a relatively low level logic network. Theparameter information or data is power supply specific whereby each ofthe power supplies is provided with the desired parameters such ascurrent, voltage and/or wire feed speed. A low level digital network canprovide the parameter information; however, the AC current for polarityreversal occurs at the same time. The “same” time indicates a timedifference of less than 10 μs and preferably in the general range of 1-5μs. To accomplish precise coordination of the AC output from powersupply 30 and power supply 32, the switching points and polarityinformation cannot be provided from a general logic network wherein thetiming is less precise. The individual AC power supplies are coordinatedby high speed, highly accurate DC logic interface referred to as“gateways.” As shown in FIG. 1, power supplies 30, 32 are provided withthe necessary operating parameters indicated by the bi-directional leads42 m, 42 s, respectively. This non-time sensitive information isprovided by a digital network shown in FIG. 1. Master power supply 30receives a synchronizing signal as indicated by unidirectional line 40to time the controller's operation of its AC output current. Thepolarity of the AC current for power supply 30 is outputted as indicatedby line 46. The actual switching command for the AC current of masterpower supply 30 is outputted on line 44. The switch command tells powersupply S, in the form of an inverter, to “kill,” which is a drasticreduction of current. In an alternative, this is actually a switchsignal to reverse polarity. The “switching points” or command on line 44preferably is a “kill” and current reversal commands utilizing the“switching points” as set forth in Stava U.S. Pat. No. 6,111,216. Thus,timed switching points or commands are outputted from power supply 30 byline 44. These switching points or commands may involve a power supply“kill” followed by a switch ready signal at a low current or merely acurrent reversal point. The switch “ready” is used when the “kill”concept is implemented because neither of the inverters are to actuallyreverse until they are below the set current. This is described in FIG.16. The polarity of the switches of controller 30 controls the logic online 46. Slave power supply 32 receives the switching point or commandlogic on line 44 b and the polarity logic on line 46 b. These two logicsignals are interconnected between the master power supply and the slavepower supply through the highly accurate logic interface shown asgateway 50, the transmitting gateway, and gateway 52, the receivinggateway on lines 44 a, 46 a. These gateways are network interface cardsfor each of the power supplies so that the logic on lines 44 b, 46 b aretimed closely to the logic on lines 44, 46, respectively. In practice,network interface cards or gateways 50, 52 control this logic to within10 μs and preferably within 1-5 μs. A low accuracy network controls theindividual power supplies for data from central control 18 through lines42 m, 42 s, illustrated as provided by the gateways or interface cards.These lines contain data from remote areas (such as central control 18)which are not time sensitive and do not use the accuracy characteristicsof the gateways. The highly accurate data for timing the switch reversaluses interconnecting logic signals through network interface cards 50,52. The system in FIG. 1 is a single cell for a single AC arc; however,the invention is not limited to tandem electrodes wherein two or more ACarcs are created to fill the large gap found in pipe welding. However,the background system is shown for this application. Thus, the masterpower supply 30 for the first electrode receives a synchronizationsignal which determines the timing or phase operation of the system Sfor a first electrode, i.e. ARC 1. System S is used with other identicalsystems to generate ARCs 2, 3, and 4 timed by synchronizing outputs 84,86, and 88. This concept is schematically illustrated in FIG. 5. Thesynchronizing or phase setting signals 82-88 are shown in FIG. 1 withonly one of the tandem electrodes. An information network N comprising acentral control computer and/or web server 60 provides digitalinformation or data relating to specific power supplies in severalsystems or cells controlling different electrodes in a tandem operation.Internet information 62 is directed to a local area network in the formof an Ethernet network 70 having local interconnecting lines 70 a, 70 b,70 c. Similar interconnecting lines are directed to each power supplyused in the four cells creating ARCs 1, 2, 3, and 4 of a tandem weldingoperation. The description of system or cell S applies to each of thearcs at the other electrodes. If AC current is employed, a master powersupply is used. In some instances, merely a master power supply is usedwith a cell specific synchronizing signal. If higher currents arerequired, the systems or cells include a master and slave power supplycombination as described with respect to system S of FIG. 1. In someinstances, a DC arc is used with two or more AC arcs synchronized bygenerator 80. Often the DC arc is the leading electrode in a tandemelectrode welding operation, followed by two or more synchronized ACarcs. A DC power supply need not be synchronized, nor is there a needfor accurate interconnection of the polarity logic and switching pointsor commands. Some DC powered electrodes may be switched between positiveand negative, but not at the frequency of an AC driven electrode.Irrespective of the make-up of the arcs, Ethernet or local area network70 includes the parameter information identified in a coded fashiondesignated for specific power supplies of the various systems used inthe tandem welding operation. This network also employs synchronizingsignals for the several cells or systems whereby the systems can beoffset in a time relationship. These synchronizing signals are decodedand received by a master power supply as indicated by line 40 in FIG. 1.In this manner, the AC arcs are offset on a time basis. Thesesynchronizing signals are not required to be as accurate as theswitching points through network interface cards or gateways 50, 52.Synchronizing signals on the data network are received by a networkinterface in the form of a variable pulse generator 80. The generatorcreates offset synchronizing signals in lines 84, 86, and 88. Thesesynchronizing signals dictate the phase of the individual alternatingcurrent cells for separate electrodes in the tandem operation.Synchronizing signals can be generated by interface 80 or actuallyreceived by the generator through the network 70. Network 70 merelyactivates generator 80 to create the delay pattern for the manysynchronizing signals. Also, generator 80 can vary the frequency of theindividual cells by frequency of the synchronizing pulses if thatfeature is desired in the tandem welding operation.

A variety of controllers and power supplies could be used for practicingthe system as described in FIG. 1; however, preferred implementation ofthe system is set forth in FIG. 2 wherein power supply PSA is combinedwith controller and power supply 30 and power supply PSB is combinedwith controller and power supply 32. These two units are essentially thesame in structure and are labeled with the same numbers whenappropriate. Description of power supply PSA applies equally to powersupply PSB. Inverter 100 has an input rectifier 102 for receiving threephase line current L1, L2, and L3. Output transformer 110 is connectedthrough an output rectifier 112 to tapped inductor 120 for drivingopposite polarity switches Q1, Q2. Controller 140 a of power supply PSAand controller 140 b of PSB are essentially the same, except controller140 a outputs timing information to controller 140 b. Switching pointsor lines 142, 144 control the conductive condition of polarity switchesQ1, Q2 for reversing polarity at the time indicated by the logic onlines 142, 144, as explained in more detail in Stava U.S. Pat. No.6,111,216 incorporated by reference herein. The control is digital witha logic processor; thus, A/D converter 150 converts the currentinformation on feedback line 16 or line 26 to controlling digital valuesfor the level of output from error amplifier 152 which is illustrated asan analog error amplifier. In practice, this is a digital system andthere is no further analog signal in the control architecture. Asillustrated, however, amplifier has a first input 152 a from converter150 and a second input 152 b from controller 140 a or 140 b. The currentcommand signal on line 152 b includes the wave shape or waveformrequired for the AC current across the arc at weld station WS. This isstandard practice as taught by several patents of Lincoln Electric, suchas Blankenship U.S. Pat. No. 5,278,390, incorporated by reference. Seealso Stava U.S. Pat. No. 6,207,929, incorporated by reference. Theoutput from amplifier 152 is converted to an analog voltage signal byconverter 160 to drive pulse width modulator 162 at a frequencycontrolled by oscillator 164, which is a timer program in the processorsoftware. The shape of the waveform at the arcs is the voltage ordigital number at lines 152 b. The frequency of oscillator 164 isgreater than 18 kHz. The total architecture of this system is digitizedin the preferred embodiment of the present invention and does notinclude reconversion back into analog signal. This representation isschematic for illustrative purposes and is not intended to be limitingof the type of power supply used in practicing the present invention.Other power supplies could be employed.

A background system utilizing the concepts of FIGS. 1 and 2 areillustrated in FIGS. 3 and 4. Workpiece 200 is a seam in a pipe which iswelded together by tandem electrodes 202, 204, and 206 powered byindividual power supplies PS1, PS2, PS3, respectively. The powersupplies can include more than one power source coordinated inaccordance with the technology in Houston U.S. Pat. No. 6,472,634. Theillustrated embodiment involves a DC arc for lead electrode 202 and anAC arc for each of the tandem electrodes 204, 206. The created waveformsof the tandem electrodes are AC currents and include shapes created by awave shaper or wave generator in accordance with the previouslydescribed waveform technology. As electrodes 202, 204 and 206 are movedalong weld path WP a molten metal puddle P is deposited in pipe seam 200with an open root portion 210 followed by deposits 212, 214, and 216from electrodes 202, 204, and 206, respectively. As previously describedmore than two AC driven electrodes as will be described and illustratedby the waveforms of FIG. 15, can be operated by the invention relatingto AC currents of adjacent electrodes. The power supplies, as shown inFIG. 4, each include an inverter 220 receiving a DC link from rectifier222. In accordance with Lincoln waveform technology, a chip or internalprogrammed pulse width modulator stage 224 is driven by an oscillator226 at a frequency greater than 18 kHz and preferably greater than 20kHz. As oscillator 226 drives pulse width modulator 224, the outputcurrent has a shape dictated by the wave shape outputted from waveshaper 240 as a voltage or digital numbers at line 242. Output leads217, 218 are in series with electrodes 202, 204, and 206. The shape inreal time is compared with the actual arc current in line 232 from Halleffect transducer 228 by a stage illustrated as comparator 230 so thatthe outputs on line 234 control the shape of the AC waveforms. Thedigital number or voltage on line 234 determines the output signal online 224 a to control inverter 220 so that the waveform of the currentat the arc follows the selected profile outputted from wave shaper 240.This is standard Lincoln waveform technology, as previously discussed.Power supply PS1 creates a DC arc at lead electrode 202; therefore, theoutput from wave shaper 240 of this power supply is a steady stateindicating the magnitude of the DC current. The present invention doesnot relate to the formation of a DC arc. To the contrary, the presentinvention is the control of the current at two adjacent AC arcs fortandem electrodes, such as electrodes 204, 206. In accordance with theinvention, wave shaper 240 involves an input 250 employed to select thedesired shape or profile of the AC waveform. This shape can be shiftedin real time by an internal programming schematically represented asshift program 252. Wave shaper 240 has an output which is a polaritysignal on line 254. In practice, the polarity signal is a bit of logic,as shown in FIG. 7. Logic 1 indicates a negative polarity for thewaveform generated by wave shaper 240 and logic 0 indicates a positivepolarity. This logic signal or bit controller 220 directed to the powersupply is read in accordance with the technology discussed in FIG. 16.The inverter switches from a positive polarity to a negative polarity,or the reverse, at a specific “READY” time initiated by a change of thelogic bit on line 254. In practice, this bit is received from variablepulse generator 80 shown in FIG. 1 and in FIG. 5. The background weldingsystem shown in FIGS. 3 and 4 uses the shapes of AC arc currents atelectrodes 204 and 206 to obtain a beneficial result, i.e. a generallyquiescent molten metal puddle P and/or synthesized sinusoidal waveformscompatible with transformer waveforms used in arc welding. The electricarc welding system shown in FIGS. 3 and 4 have a program to select thewaveform at “SELECT” program 250 for wave shaper 240. The uniquewaveforms are used by the tandem electrodes. One of the power suppliesto create an AC arc is schematically illustrated in FIG. 5. The powersupply or source is controlled by variable pulse generator 80, shown inFIG. 1. Signal 260 from the generator controls the power supply for thefirst arc. This signal includes the synchronization of the waveformtogether with the polarity bit outputted by the wave shaper 240 on line254. Lines 260 a-260 n control the desired subsequent tandem AC arcsoperated by the welding system of the present invention. The timing ofthese signals shifts the start of the other waveforms. FIG. 5 merelyshows the relationship of variable pulse generator 80 to control thesuccessive arcs as explained in connection with FIG. 4.

In the welding system of Houston U.S. Pat. No. 6,472,634, the ACwaveforms are created as shown in FIG. 6 wherein the wave shaper for arcAC1 at electrode 204 creates a signal 270 having positive portions 272and negative portions 274. The second arc AC2 at electrode 206 iscontrolled by signal 280 from the wave shaper having positive portions282 and negative portions 284. These two signals are the same, but areshifted by the signal from generator 80 a distance x, as shown in FIG.6. The waveform technology created current pulses or waveforms at one ofthe arcs are waveforms having positive portions 290 and negativeportions 292 shown at the bottom portion of FIG. 6. A logic bit from thewave shaper determines when the waveform is switched from the positivepolarity to the negative polarity and the reverse. In accordance withthe disclosure in Stava U.S. Pat. No. 6,111,216 (incorporated byreference herein) pulse width modulator 224 is generally shifted to alower level at point 291 a and 291 b. Then the current reduces untilreaching a fixed level, such as 100 amps. Consequently, the switcheschange polarity at points 294 a and 294 b. This produces a vertical lineor shape 296 a, 296 b when current transitioning between positiveportion 290 and negative portion 292. This is the system disclosed inthe Houston patent where the like waveforms are shifted to avoidmagnetic interference. The waveform portions 290, 292 are the same atarc AC1 and at arc AC2. This is different from the present inventionwhich relates to customizing the waveforms at arc AC1 and arc AC2 forpurposes of controlling the molten metal puddle and/or synthesizing asinusoidal wave shape in a manner not heretofore employed. Thedisclosure of FIG. 6 is set forth to show the concept of shifting thewaveforms. The same switching procedure to create a vertical transitionbetween polarities is used in the preferred embodiment of the presentinvention. Converting from the welding system shown in FIG. 6 to animbalance waveform is generally shown in FIG. 7. The logic on line 254is illustrated as being a logic 1 in portions 300 and a logic 0 inportions 302. The change of the logic or bit numbers signals the timewhen the system illustrated in FIG. 16 shifts polarity. This isschematically illustrated in the lower graph of FIG. 6 at points 294 a,294 b. Wave shaper 240 for each of the adjacent AC arcs has a first waveshape 310 for one of the polarities and a second wave shape 312 for theother polarity. Each of the waveforms 310, 312 are created by the logicon line 234 taken together with the logic on line 254. Thus, pulses 310,312 as shown in FIG. 7, are different pulses for the positive andnegative polarity portions. Each of the pulses 310, 312 are created byseparate and distinct current pulses 310 a, 312 a as shown. Switchingbetween polarities is accomplished as illustrated in FIG. 6 where thewaveforms generated by the wave shaper are shown as having the generalshape of waveforms 310, 312. Positive polarity controls penetration andnegative polarity controls deposition. The positive and negative pulsesof a waveform are different and the switching points are controlled sothat the AC waveform at one arc is controlled both in the negativepolarity and the positive polarity to have a specific shape created bythe output of wave shaper 240. The waveforms for the arc adjacent to thearc having the current shown in FIG. 7 is controlled differently toobtain the advantages illustrated best in FIG. 8. The waveform at arcAC1 is in the top part of FIG. 8. It has positive portions 320 shown bycurrent pulses 320 a and negative portions 322 formed by pulses 322 a.Positive portion 320 has a maximum magnitude a and width or time periodb. Negative portion 322 has a maximum magnitude d and a time or periodc. These four parameters are adjusted by wave shaper 240. In theillustrated embodiment, arc AC2 has the waveform shown at the bottom ofFIG. 8 where positive portion 330 is formed by current pulses 330 a andhas a height or magnitude a′ and a time length or period b′. Negativeportion 332 is formed by pulses 332 a and has a maximum amplitude d′ anda time length c′. These parameters are adjusted by wave shaper 240. Inaccordance with the invention, the waveform from the wave shaper on arcAC1 is out of phase with the wave shape for arc AC2. The two waveformshave parameters or dimensions which are adjusted so that (a) penetrationand deposition is controlled and (b) there is no long time during whichthe puddle P is subjected to a specific polarity relationship, be it alike polarity or opposite polarity. This concept in formulating the waveshapes prevents long term polarity relationships as explained by theshowings in FIGS. 9 and 10. In FIG. 9 electrodes 204, 206 have likepolarity, determined by the waveforms of the adjacent currents at anygiven time. At that instance, magnetic flux 350 of electrode 204 andmagnetic flux 352 of electrode 206 are in the same direction and canceleach other at center area 354 between the electrodes. This causes themolten metal portions 360, 362 from electrodes 204, 206 in the moltenpuddle P to move together, as represented by arrows c. This inwardmovement together or collapse of the molten metal in puddle P betweenelectrodes 204 will ultimately cause an upward gushing action, if notterminated in a very short time, i.e. less than about 20 ms. As shown inFIG. 10, the opposite movement of the puddle occurs when the electrodes204, 206 have opposite polarities. Then, magnetic flux 370 and magneticflux 372 are accumulated and increased in center portion 374 between theelectrodes. High forces between the electrodes causes the molten metalportions 364, 366 of puddle P to retract or be forced away from eachother. This is indicated by arrows r. Such outward forcing of the moltenmetal in puddle P causes disruption of the weld bead if it continues fora substantial time which is generally less than 10 ms. As can be seenfrom FIGS. 9 and 10, it is desirable to limit the time during which thepolarity of the waveform at adjacent electrodes is either the samepolarity or opposite polarity. The waveform, such as shown in FIG. 6,accomplishes the objective of preventing long term concurrence ofspecific polarity relationships, be it like polarities or oppositepolarities. As shown in FIG. 8, like polarity and opposite polarity isretained for a very short time less than the cycle length of thewaveforms at arc AC1 and arc AC2. This positive development ofpreventing long term occurrence of polarity relationships together withthe novel concept of pulses having different shapes and differentproportions in the positive and negative areas combine to control thepuddle, control penetration and control deposition in a manner notheretofore obtainable in welding with a normal transformer powersupplies or normal use of Lincoln waveform technology.

In FIG. 11 the positive and negative portions of the AC waveform fromthe wave shaper 240 are synthesized sinusoidal shapes with a differentenergy in the positive portion as compared to the negative portion ofthe waveforms. The synthesized sine wave or sinusoidal portions of thewaveforms allows the waveforms to be compatible with transformer weldingcircuits and compatible with evaluation of sine wave welding. In FIG.11, waveform 370 is at arc AC1 and waveform 372 is at arc AC2. Thesetandem arcs utilize the AC welding current shown in FIG. 11 wherein asmall positive sinusoidal portion 370 a controls penetration at arc AC1while the larger negative portion 370 b controls the deposition of metalat arc AC1. There is a switching between the polarities with a change inthe logic bit, as discussed in FIG. 7. Sinusoidal waveform 370 plungesvertically from approximately 100 amperes through zero current as shownin vertical line 370 c. Transition between the negative portion 370 band positive portion 370 a also starts a vertical transition at theswitching point causing a vertical transition 370 d. In a like manner,phase shifted waveform 372 of arc AC2 has a small penetration portion372 a and a large negative deposition portion 372 b. Transition betweenpolarities is indicated by vertical lines 372 c and 372 d. Waveform 372is shifted with respect to waveform 370 so that the dynamics of thepuddle are controlled without excessive collapsing or repulsion of themolten metal in the puddle caused by polarities of adjacent arcs AC1,AC2. In FIG. 11, the sine wave shapes are the same and the frequenciesare the same. They are merely shifted to prevent a long term occurrenceof a specific polarity relationship.

In FIG. 12 waveform 380 is used for arc AC1 and waveform 382 is used forarc AC2. Portions 380 a, 380 b, 382 a, and 382 b are sinusoidalsynthesized and are illustrated as being of the same general magnitude.By shifting these two waveforms 90°, areas of concurrent polarity areidentified as areas 390, 392, 394, and 396. By using the shiftedwaveforms with sinusoidal profiles, like polarities or oppositepolarities do not remain for any length of time. Thus, the molten metalpuddle is not agitated and remains quiescent. This advantage is obtainedby using the present invention which also combines the concept of adifference in energy between the positive and negative polarity portionsof a given waveform. FIG. 12 is illustrative in nature to show thedefinition of concurrent polarity relationships and the fact that theyshould remain for only a short period of time. To accomplish thisobjective, another embodiment of the present invention is illustrated inFIG. 13 wherein previously defined waveform 380 is combined withwaveform 400, shown as the sawtooth waveform of arc AC2(a) or thepulsating waveform 402 shown as the waveform for arc AC2(b). Combiningwaveform 380 with the different waveform 400 of a different waveform 402produces very small areas or times of concurrent polarity relationships410, 412, 414, etc. In FIG. 14 the AC waveform generated at one arc isdrastically different than the AC waveform generated at the other arc.This same concept of drastically different waveforms for use in thepresent invention is illustrated in FIG. 14 wherein waveform 420 is anAC pulse profile waveform and waveform 430 is a sinusoidal profilewaveform having about one-half the period of waveform 420. Waveform 420includes a small penetration positive portion 420 a and a largedeposition portion 420 b with straight line polarity transitions 420 c.Waveform 430 includes positive portion 430 a and negative portion 430 bwith vertical polarity transitions 430 c. By having these two differentwaveforms, both the synthesized sinusoidal concept is employed for oneelectrode and there is no long term concurrent polarity relationship.Thus, the molten metal in puddle P remains somewhat quiescent during thewelding operation by both arcs AC1, AC2.

In FIG. 15 waveforms 450, 452, 454, and 456 are generated by the waveshaper 240 of the power supply for each of four tandem arcs, arc AC1,arc AC2, arc AC3, and arc AC4. The adjacent arcs are aligned asindicated by synchronization signal 460 defining when the waveformscorrespond and transition from the negative portion to the positiveportion. This synchronization signal is created by generator 80 shown inFIG. 1, except the start pulses are aligned. In this embodiment of theinvention first waveform 450 has a positive portion 450 a, which issynchronized with both the positive and negative portion of the adjacentwaveform 452, 454, and 456. For instance, positive portion 450 a issynchronized with and correlated to positive portion 452 a and negativeportion 452 b of waveform 452. In a like manner, the positive portion452 a of waveform 452 is synchronized with and correlated to positiveportion 454 a and negative portion 454 b of waveform 454. The samerelationship exists between positive portion 454 a and the portions 456a, 456 b of waveform 456. The negative portion 450 b is synchronizedwith and correlated to the two opposite polarity portions of alignedwaveform 452. The same timing relationship exists between negativeportion 452 b and waveform 454. In other words, in each adjacent arc onepolarity portion of the waveform is correlated to a total waveform ofthe adjacent arc. In this manner, the collapse and repelling forces ofpuddle P, as discussed in connection with FIGS. 9 and 10, arediametrically controlled. One or more of the positive or negativeportions can be synthesized sinusoidal waves as discussed in connectionwith the waveforms disclosed in FIGS. 11 and 12.

As indicated in FIGS. 1 and 2, when the master controller of switches isto switch, a switch command is issued to master controller 140 a ofpower supply 30. This causes a “kill” signal to be received by themaster so a kill signal and polarity logic is rapidly transmitted to thecontroller of one or more slave power supplies connected in parallelwith a single electrode. If standard AC power supplies are used withlarge snubbers in parallel with the polarity switches, the slavecontroller or controllers are immediately switched within 1-10 μs afterthe master power supply receives the switch command. This is theadvantage of the high accuracy interface cards or gateways. In practice,the actual switching for current reversal of the paralleled powersupplies is not to occur until the output current is below a givenvalue, i.e. about 100 amperes. This allows use of smaller switches.

The implementation of the switching for all power supplies for a singleAC arc uses the delayed switching technique where actual switching canoccur only after all power supplies are below the given low currentlevel. The delay process is accomplished in the software of the digitalprocessor and is illustrated by the schematic layout of FIG. 16. Whenthe controller of master power supply 500 receives a command signal asrepresented by line 502, the power supply starts the switching sequence.The master outputs a logic on line 504 to provide the desired polarityfor switching of the slaves to correspond with polarity switching of themaster. In the commanded switch sequence, the inverter of master powersupply 500 is turned off or down so current to electrode E is decreasedas read by Hall effect transducer 510. The switch command in line 502causes an immediate “kill” signal as represented by line 512 to thecontrollers of paralleled slave power supplies 520, 522 providingcurrent to junction 530 as measured by Hall effect transducers 532, 534.All power supplies are in the switch sequence with inverters turned offor down. Software comparator circuits 550, 552, 554 compare thedecreased current to a given low current referenced by the voltage online 556. As each power supply decreases below the given value, a signalappears in lines 560, 562, and 564 to the input of a sample and holdcircuits 570, 572, and 574, respectively. The circuits are outputted bya strobe signal in line 580 from each of the power supplies. When a setlogic is stored in a circuit 570, 572, and 574, a YES logic appears onlines READY¹, READY², and READY³ at the time of the strobe signal. Thissignal is generated in the power supplies and has a period of 25 μs;however, other high speed strobes could be used. The signals aredirected to controller C of the master power supply, shown in dashedlines in FIG. 16. A software ANDing function represented by AND gate 584has a YES logic output on line 582 when all power supplies are ready toswitch polarity. This output condition is directed to clock enableterminal ECLK of software flip flop 600 having its D terminal providedwith the desired logic of the polarity to be switched as appearing online 504. An oscillator or timer operated at about 1 MHz clocks flipflop by a signal on line 602 to terminal CK. This transfers the polaritycommand logic on line 504 to a Q terminal 604 to provide this logic inline 610 to switch slaves 520, 522 at the same time the identical logicon line 612 switches master power supply 500. After switching, thepolarity logic on line 504 shifts to the opposite polarity while masterpower supply awaits the next switch command based upon the switchingfrequency. Other circuits can be used to affect the delay in theswitching sequence; however, the illustration in FIG. 16 is the presentscheme.

As so far described in FIGS. 1-16, the welder, and control system forthe welder to accomplish other advantageous features is submitted asbackground information. This description explains the background, notprior art, to the present invention. This background technology has beendeveloped by The Lincoln Electric Company, assignee of the presentapplication. This background description is not necessarily prior art,but is submitted for explanation of the specific improvement in suchwaveform technology welders, as accomplished by the welder described inFIG. 17. This welder “paints” the exact profile of a waveform to be usedin a welding process. Thus, a precise waveform is obtained by use ofprogram 700. This waveform is coordinated with a specific coredelectrode.

The welder and/or welding system as shown in FIGS. 4 and 5, is operatedby control program 700 used to accurately set the exact profile of agiven waveform for use with a specific cored electrode shown in FIGS. 19and 20. Program 700 is illustrated in FIG. 17, where welder 705 has awave shaper 240 set to a general type of weld waveform by a selectnetwork 250. The selected waveform is the desired AC waveform toperform, by a succession of waveforms, a given welding process. Thiswaveform, in accordance with the invention, is set to be used with aspecific cored electrode. Waveform control program 700 has a profilecontrol network 710 to set the exact, desired profile of the waveformand a magnitude control circuit 712 to adjust the energy or power of thewaveform without substantially changing the set profile to be used for agiven cored electrode. This specific profile is stored in the welderdisclosed in FIGS. 21 and 28 for use when the corresponding electrode isto be used in the welding process.

The program or control network 700 is connected to the wave shaper 240to control the exact general profile of each individual waveform in thesuccession of waveforms constituting an AC welding process. Toaccomplish this objective of accurate and precise synergic setting ofthe waveform general profile, four separate profile parameters areadjusted individually. The first parameter is frequency set into thewaveform profile by circuit 720 manually or automatically adjusted byinterface network 722 to produce a set value on an output represented asline 724. This value controls the set frequency of the waveform profile.Of course, this is actually the period of the waveform. In a likemanner, the duty cycle of the waveform is controlled by circuit 730having an adjustable interface network 732 and an output line 734 fordeveloping a value to control the relationship between the positive halfcycle and the negative half cycle. This profile parameter is set by thelogic or data on line 734 from circuit 730. By the signal or data online 724 and the data on line 734, the AC profile of the waveform isset. This does not relate to the energy level of the individual portionsof the waveform, but merely the general fixed profile of the waveform.To control the up ramp rate of the waveform there is provided a circuit742 having a manual or automatic adjusting network 742 and an outputsignal on line 744 for setting the rate at which the set profile of thewaveform changes from negative to a positive polarity. In a like manner,a down ramp circuit 750 is provided with an adjusting interface 752 andan output line 754. The magnitudes of the values on lines 724, 734, 744and 754 set the profile of the individual waveform. At least two ofthese parameter profiles are set together; however, preferably all ofthe profile parameters are set to define a waveform profile.

To control the profile of the waveform for the purposes of the energy orpower transmitted by each individual waveform in the welding process,program 700 includes magnitude circuit or network 712 divided into twoindividual sections 760, 762. These sections of the magnitude circuitcontrol the energy or other power related level of the waveform duringeach of the polarities without substantially affecting the generalprofile set by profile control network 710. Section 760 includes a levelcontrol circuit 770 which is manually adjusted by an interface network772 to control the relationship between an input value on line 774 andan output value on line 776. Level control circuit 770 is essentially adigital error amplifier circuit for controlling the current, voltageand/or power during the positive portion of the generated set waveformprofile. Selector 250 a shifts circuit 770 into either the current,voltage or power mode. Section 760 controls the energy, or power orother heat level during the positive portion of the waveform withchanging the general profile set by network 710. In a like manner,second section 762 has a digital error amplifier circuit 780 that is setor adjusted by network 782 so that the value on input line 784 controlsthe level or signal on output line 786. Selector 250 b shifts circuit780 into either the current, voltage or power mode. Consequently, thedigital level data on lines 776 and 786 controls the current, voltageand/or power during each of the half cycles set by profile controlnetwork 710.

In accordance with another feature of program 700, wave shaper 240 iscontrolled by only magnitude control circuit 712 and the profile is setby network or program 250 used in the background system shown in FIGS. 4and 5. Network 250 does not set the profile, but selects known types ofwaveforms as will be explained with the disclosure of FIGS. 21 and 28.The enhanced advantage of program 700 is realized by setting all profileparameters using circuits 720, 730, 740, and 750 together with themagnitude circuits 770, 780. Of course, a waveform controlled by any oneof these circuits is an improvement over the background technology.Program 700 synergically adjusts all profile parameters and magnitudevalues during each polarity of the AC waveform so the waveformcorresponds to a specific cored electrode.

To explain the operation of program 700, two waveforms are schematicallyillustrated in FIG. 18. Waveform 800 has a positive portion 802 and anegative portion 804, both produced by a series of rapidly createdcurrent pulses 800 a. Waveform 800 is illustrated as merely a squarewave to illustrate control of the frequency or period of the waveformand the ratio of the positive portion 802 to the negative portion 804.These parameters are accurately set by using program 700 to modify thetype of waveform heretofore merely selected by network 450. In thisschematic representation of the waveform, the up ramp rate and the downramp rate are essentially zero. Of course, the switching concept taughtin Stava U.S. Pat. No. 6,111,216 would be employed for shifting betweenpositive and negative waveform portions to obtain the advantagesdescribed in the Stava patent. Second illustrated waveform 810 has afrequency f, a positive portion 812 and a negative portion 814. In thisillustration, the up ramp rate 816 is controlled independently of thedown ramp rate 818. These ramp rates are illustrated as arrows toindicate they exist at the leading and trailing edges of the waveformduring shifts between polarities. Program 700 relates to physicallysetting the exact profile of the individual waveforms by circuits 720,730, 740, and 750. Several parameters of the waveform are adjusted toessentially “paint” the waveform into a desired profile. A very precisewelding process using a set general profile for the AC waveform isperformed by a waveform technology controlled welder using program 700.This program is used to “paint” a waveform for each individual coredelectrode so there is a match between the AC waveform and the electrodeused in the welding process.

Program 700 in FIG. 17 is used to construct or create AC waveforms thatare optimized and specially tailored for each of individually identifiedcored electrode such as electrode 910 shown in FIGS. 19 and 20. A welder900 has torch 902 for directing electrode 910 toward workpiece W. An arcAC is created between the end of electrode 910 and workpiece W. Theelectrode is a cored electrode with sheath 912 and internal filled core914. The core includes flux ingredients, such as represented byparticles 914 a. The purpose of these ingredients 914 a is to (a) shieldthe molten weld metal from atmospheric contamination by covering themolten metal with slag, (b) combine chemically with any atmosphericcontaminants such that their negative impact on the weld quality isminimized and/or (c) generate arc shielding gases. In accordance withstandard practice, core 914 also includes alloying ingredients, referredto as particles 914 b, together with other miscellaneous particles 914 cthat are combined to provide the fill of core 914. To optimize thewelding operation, it has been necessary to use solid wire with anexternal shielding gas. However, in order to produce a weld withspecific mechanical and metallurgical properties, specific alloys arerequired, which can be difficult to obtain in the form of a solid wire.Contamination is difficult to prevent when using a welding processrequiring external shielding gas. It would be advantageous to thereforeuse a self shielding cored electrode, so that the environment does notaffect the welding. Cored electrodes experience different burn backrates for the sheath and core. All of these difficulties have resultedin most pipeline welding to be done with a solid wire and externalshielding gas. To overcome these problems, STT welding was developed byThe Lincoln Electric Company of Cleveland, Ohio for use in pipelinewelding. Such welding employs a short circuit process where surfacetension transfers the molten metal. This process did lower heat of thewelding process, especially during open root welding. The advantages ofboth welding with an AC power source and cored electrodes were notobtainable because the welding waveforms were not optimized for thespecific cored electrode. The present invention overcomes thesedifficulties by using a program such as program 700 shown in FIG. 17 soa precise AC waveform is generated for the welding operation andcorrelated specifically to a given cored electrode. By providing aprecisely profiled or shaped waveform for an AC welding operationcoordinated with a given cored electrode the welding operation isoptimized. It is now possible to use an AC welding operation with awaveform accurately profiled to accommodate a specific cored electrode.

Welder 900 is constructed in accordance with the present invention forperforming an AC welding operation using a cored electrode so thewelding operation is optimized for the particular electrode. Details ofwelder 900 are shown in FIG. 21 where power source 920 is driven byrectifier 920 a. Electrode 910 is a cored electrode with sheath 912 andcore 914. Power source 920 of welder 900 has a storage device, unit orcircuit 922 to create an electrode identification signal in line 924 toidentify a particular electrode 910 being used in the welding process.Reading device 921 identifies the particular electrode 910 passing bythe reading device as indicated at the top of FIG. 21. Thus, the signalin line 924 identifies electrode 910. Device 921 a manually tellsreading device 921 which particular electrode 910 is being used. Inother words, reading device 921 is set to the particular cored electrode910 to be used in the welding operation. This device is manuallyadjusted to indicate a specific electrode. Electrode 910 can beidentified by storage device 922 by a bar code or other readingtechnique. The bar code is located on the spool or drum containingelectrode wire 910. In other words, device 921 either automaticallysenses the identification of wire or electrode 910 or receives manualinput to indicate the electrode as indicated by block 921 a. A signal in921 b is directed to storage device 922 where a signal in data form isstored for all electrodes to be used by welder 900. The signal on line921 b addresses a particular data in storage device 922 correspondingwith the specific cored electrode. This data causes an electrodeidentification signal to be applied to line 924. This signal 924activates waveform look up device 926 so the device outputs a profilesignal in line 928. This signal 928 instructs select circuit 250 toselect a particular stored profile which has been created by program 700for a particular cored electrode. Program 700 shown in FIG. 17 tailorsthe stored waveforms to a specific electrode. The remainder of powersource 920 has been previously described. The profile signal in line 928selects a specific constructed or created waveform stored in a memoryassociated with circuit 250. An AC welding waveform tailored to theparticular construction and constituents of a particular cored electrode910 is outputted in line 242. In accordance with an alternative, theparticular signal in line 928 is determined by the electrode and thewire feed speed. Device 930 has a set point that is outputted in line932. Consequently, the logic or data on lines 924 and 932 determine theprofile select signal in line 928. A desired stored profile in thememory of waveform generator 250 is used. This profile is based upon theparticular electrode and/or the particular set point wire feed speed.

A typical constructed AC waveform is illustrated in FIG. 22 whereprocess curve 950 includes a series of waveforms comprising positivesection 952 and negative section 954. In accordance with the invention,the waveforms are created by a large number of individual pulses 960created at a rate substantially greater than 18 kHz and created at theoutput line 224 a of pulse width modulator 224. This controls the highswitching speed inverter. In the preferred embodiment of the invention,curve 950 has a positive magnitude x and a negative magnitude y with thelength of the negative portion 954 indicated to be z. In order tocontrol the heat in the welding operation, duty cycle z is adjusted whenthe waveform shown in FIG. 22 is constructed for a particular coredelectrode. The negative portion 954 of FIG. 22 controls the overall heatinput to the workpiece. The positive portion 952 contributes more heatto the electrode and less heat to the workpiece. Therefore, by changingthe duty cycle, the overall heat into the workpiece can be varied orcontrolled. In the present invention, an AC welding process is createdat the output of wave shaper or waveform generator 240. The selectedwaveform is precisely adjusted to optimize its use with a particularcored electrode 910. To control the heat in the welding operation, thewaveform has duty cycle of z controlled by program 700. After thewaveform has been fixed, it is set into waveform generator 240 basedupon the logic from select circuit 250. Welder 900 is used to correlatea particular AC waveform with a particular cored electrode to fix theoperation of the welding process dictated by the constituents formingelectrode 910.

The waveform used in practicing the invention is preferably a squarewaveform as shown in FIG. 22; however, to control the initial heating itis within the scope of the invention to provide a non-square AC waveformshown in FIG. 23 wherein process curve 970 comprises waveforms, eachhaving positive portion 972 and negative portion 974. Each of theseportions is formed by a plurality of individual pulses 960 as explainedwith respect to curve 950 in FIG. 22. These individual pulses 960 arecreated at a frequency greater than 18 kHz and are waveform technologypulses normally used in inverter type power sources. To reduce the rateof heating, portions 972, 974 are provided with ramp portions 976, 977,978, and 979. Other profiles are possible to optimize the AC weldingusing the present invention.

A problem caused when using cored electrodes without implementation ofthe present invention is illustrated in FIG. 24. The welding processmelts sheath 912 to provide a portion of molten metal 980 meltedupwardly around the electrode, as indicated by melted upper end 982.Thus, the sheath of the electrode is melted more rapidly than the core.This causes a molten metal material to exist at the output end ofelectrode 910 without protective gas or chemical reaction created bymelting of the internal constituents of core 914. Thus, arc AC melts themetal of electrode 910 in an unprotected atmosphere. The necessaryshielding for the molten metal is formed when the sheath and core aremelted at the same rate. The problem of melting the molten metal morerapidly than the core is further indicated by the pictorialrepresentation of FIG. 25. Molten metal 990 from sheath 912 has alreadyjoined workpiece W before the core has had an opportunity to be melted.It cannot provide the necessary shielding for the welding process. FIGS.24 and 25 show the reason why AC welding using cored electrodes has notbeen used for off-shore pipeline welding and other pipeline welding.

The invention proposes the use of an AC waveform as described above as ameans to control the heat input when using a cored electrode.

By using the present invention, the precise profile for the AC waveformused in the welding process is selected whereby sheath 912 and core 914melt at approximately the same rate. The failure to adequatelycoordinate the melting of the shield with the melting of the core wouldbe a reason for rejecting the use of AC welding with cored electrodesfor pipeline welding. The advantage of the invention is a process notneeding external shielding gas. When this occurs, shielding gas SG andother shielding constituents are generated ahead of the molten metalfrom sheath 912. By using the present invention this feature can beobtained by precisely profiling the waveform for the welding operationusing program 700. In the past such coordination was not possible.Invention of program 700 or like programs made the present inventionpossible. These programs generate waveforms which are specificallytailored for individual cored electrodes allowing cored electrodes to beused in an AC welding process in a manner to protect the molten metalagainst atmospheric contamination during the welding operation.

When welding with a cored electrode, it is desired to have the sheathand core melt at the same rate. This operation promotes homogeneousmixing of certain core materials with the outer sheath, such that themixture of molten materials chemically resists the effects ofatmospheric contamination. Alloying elements required to produce desiredweld metal mechanical and metallurgical characteristics are uniformlydistributed in the weld metal. In addition, the protective benefitsderived from slag and/or gas-forming constituents are optimized. Thissituation is illustrated in FIG. 27. In contrast, FIG. 26 illustrates asituation where the sheath has melted more rapidly than the core. Moltenmetal 990 from sheath 912 has already joined workpiece W before core 914has had an opportunity to be melted. Metal 990 has not been protectedfrom the effects of atmospheric contamination to the degree that itwould have been if the unmelted core constituents had actually beenmelted. Additionally, alloying elements needed to achieve desiredmechanical and metallurgical characteristics may be missing from moltenmetal 990.

An alternative of the present invention is shown in FIG. 27 where selectcircuit 992 selects a waveform B in accordance with the data in line 994a from block 994. This block has data identifying a particular electrodeA. The electrode has a composition that is accommodated by waveform B inselect circuit 992. A set point in line 996 a from wire feed speed block996 is used to select waveform B so that waveform B is not only awaveform for the electrode which is a primary aspect of the invention,but electrode A with a particular set point. This adjusts the output ofwaveform generator 240 to control the waveform of the AC welding processto be tailored to the exact cored electrode A identified by block 994.Electrode A is used to activate waveform B.

The basic aspect of the invention is creation of a waveform to performthe desired operation when using a particular cored electrode. Byidentifying the particular cored electrode and activating itscoordinated AC waveform, the desired welding process is performedbetween the electrode and the workpiece. Various analog and digitalcomponents are possible for performing the present invention. Theconstituents of the core and the size of the sheath determines theoptimum waveform profile used in the AC welding process. This inventionis made possible by the use of a program such as program 700 in FIG. 17to precisely set and modify the profile of the waveform being used in anelectric arc welding process of the type using waveform technology.

FIG. 27 shows an additional side view of a tandem electrode embodimentunder the disclosures herein. Electrodes 2702, 2704, 2706, and 2708 canbe controlled by the power source(s) disclosed herein. While fourelectrodes are shown here (similar to the three electrodes shown in FIG.3), it is noted that any number of adjacent electrodes can be employedwithout departing from the scope or spirit of the innovation. In FIG.27, workpiece 2700 may be a seam in a pipe which is welded together bytandem electrodes 2702, 2704, 2706, and 2708 powered by individual powersupplies PS1, PS2, PS3, and PS4, respectively. The illustratedembodiment involves a DC arc for lead electrode 2702 and an AC arc foreach of the tandem electrodes 2704, 2706, and 2708. The createdwaveforms of the tandem electrodes are AC currents and include shapescreated by a wave shaper or wave generator in accordance with thepreviously described waveform technology. As electrodes 2702, 2704,2706, and 2708 are moved along weld path WP a molten metal puddle P isdeposited in pipe seam 2700 with an open root portion 2710 followed bydeposits 2712, 2714, 2716, and 2718 from electrodes 2702, 2704, 2706,and 2708, respectively.

Having thus defined the invention, the following is claimed:
 1. Anelectric arc welder, comprising: a first electrode used in a weldingprocess; a second electrode used in the welding process that is adjacentto the first electrode; a third electrode used in the welding processthat is adjacent to the second electrode; a fourth electrode used in thewelding process that is adjacent to the third electrode; a coredelectrode reading device that identifies at least one of the firstelectrode, the second electrode, the third electrode, and the fourthelectrode; a first waveform profile that includes a positive portion anda negative portion for a duration of time in which the first waveformprofile is correlated to the first electrode based at least in part onmaterials of the first electrode, the first waveform profile is relatedto at least one of total current, voltage, or power of a waveform; asecond waveform profile that includes at least one positive portion andat least one negative portion for the duration of time in which thesecond waveform profile is correlated to the second electrode based atleast in part on materials of the second electrode, the second waveformprofile is related to at least one of a total current, voltage, or powerof a waveform; a third waveform profile that includes at least onepositive portion and at least one negative portion for the duration oftime in which the third waveform profile is correlated to the thirdelectrode based at least in part on materials of the third electrode,the third waveform profile is related to at least one of a totalcurrent, voltage, or power of a waveform; a fourth waveform profile thatincludes at least one positive portion and at least one negative portionfor the duration of time in which the fourth waveform profile iscorrelated to the fourth electrode based at least in part on materialsof the fourth electrode, the fourth waveform profile is related to atleast one of a total current, voltage, or power of a waveform; a firstpower source operative to provide a first succession of waveformsbetween the first electrode and a workpiece according to a first waveshape signal based on the first waveform profile; a second power sourceoperative to provide a first succession of wavedforms between the firstelectrode and the workpiece according to a second wave shape signalbased on the second waveform profile; a third power source operative toprovide a third succession of waveforms between the third electrode andthe workpiece according to a third wave shape signal based on the thirdwaveform profile; a fourth power source operative to provide a fourthsuccession of waveforms between the fourth electrode and the workpieceaccording to a fourth wave shape signal based on the fourth waveformprofile; and a select circuit causing at least one of said first powersource, said second power source, said third power source, and saidfourth power source to provide its respective succession of waveformsaccording to a cored electrode identification from the cored electrodereading device, at least one of the first waveform profile, the secondwaveform profile, the third waveform profile, and the fourth waveformprofile are selected to reduce concurrent polarities of adjacentelectrodes during the duration of time, at least one of the firstelectrode, the second electrode, the third electrode, and the forthelectrode respectively each comprise a sheath and a core, and whereinthe first waveform profile, the second waveform profile, the thirdwaveform profile, and the fourth waveform profile cause the respectivesheath and core of each electrode to melt at approximately the samerate.
 2. The electric welder of claim 1, further comprising: at leastone positive portion and at least one negative portion of the secondwaveform profile is synchronized and correlated to the positive portionof the first waveform profile during approximately a half of theduration of time; at least one positive portion and at least onenegative portion of the second waveform profile is synchronized andcorrelated to the negative portion of the first waveform profile duringapproximately a half of the duration of time; at least one positiveportion and at least one negative portion of the third waveform profileis synchronized and correlated to the at least one positive portion ofthe second waveform profile during approximately a quarter of theduration of time; at least one positive portion and at least onenegative portion of the third waveform profile is synchronized andcorrelated to the at least one negative portion of the second waveformprofile during approximately a quarter of the duration of time; at leastone positive portion and at least one negative portion of the fourthwaveform profile is synchronized and correlated to the at least onepositive portion of the third waveform profile during approximately aneighth of the duration of time; and at least one positive portion and atleast one negative portion of the fourth waveform profile issynchronized and correlated to the at least one negative portion of thethird waveform profile during approximately an eighth of the duration oftime.
 3. The electric welder of claim 1, further comprising an electrodeidentification signal operative to identify the first electrode, thesecond electrode, the third electrode, and the fourth electrode.
 4. Theelectric welder of claim 3, wherein one or more of the first waveformprofile, the second waveform profile, the third waveform profile, andthe fourth waveform profile is selected based on the identificationsignal.